I’m practicing the implementation of Linked list code. so I write the code:

file LinkedList.c

#include <stdio.h>
#include "function.h"
int main(void) {
    //initialize
    struct Node myNode = { 10,NULL };
    List head = &myNode;
    insert(20, head, head);
   
    makeEmpty(head);
   
    return 0;
}

file function.h

//this is the statement of the Linkedlist
#ifndef _FUNCTION_H
#define _FUNCTION_H
struct Node;

//pointer to the strcut Node
typedef struct Node* PtrToNode;
typedef PtrToNode List;
typedef PtrToNode Position;

struct Node
{
    //a struct pointer that point to next struct
    int element;
    //body
    Position Next;
    /* data */
};


//清空整张链表
List makeEmpty(List L);
//判断链表是否为空
int isEmpty(List L);
int isLast(Position p, List L);
Position Find(void* x, List L);
void insert(int x, List L, Position P);

#endif /*_function_h*/

file List.c

#include "function.h"
#include <stdio.h>
#include <stdlib.h>
List makeEmpty(List L) {
    Position cur = L;
    Position next;
    while (cur!= NULL) {
        next = cur->Next;
        free(cur); 
        cur = next;
    }
    cur = NULL;
    next = NULL;
    //这里c是copy by value 所以改变那个指针，如果不赋值的话
    //就是用void的话，不会将原来的指针改变。
    L = NULL;
    return L;
}

//right
int  isEmpty(List L) {
    return L->Next == NULL;
}

int isLast(Position P, List L) {

    //判断P在不在List里
    List cur = L;
    while (cur->Next != P) {
        cur = cur->Next;
    }
    if (cur == NULL) {
        fprintf(stderr, "there is no P in the  list Ln");
        return  -1;
    }

    if (P->Next == NULL) {
        return 1;
    }
    else {
        return 0;
    }
    return -1;
}

void insert(int x, List L, Position P) {
    Position tmpCell;
    tmpCell = (Position)malloc(sizeof(struct Node));
    if (tmpCell == NULL) {
        fprintf(stderr,"out of the space!n");
    }
    tmpCell->element = x;
    tmpCell->Next = P->Next;
    P->Next = tmpCell;
}

but when I run the code , I get the fault that : invalid heap pointer , so why

,and when I write head->Next as the parameter in the function “makeEmpty” ,it can run ,but why, in my program , “head” point to the first struct, so head->Next should point to the second struct. I’m really puzzled.